Attempting to stay fit — especially over the holidays — can be a tough task. The Tinke Wellness Monitor ($120) can help. This diminutive device connects to the bottom of your iPhone* and has you place your thumb on its sensing platform, where it detects changes in skin blood volume to give you a real-time look at heart rate, heart rate variability, respiratory rate, and blood oxygen saturation. Thanks to the free app, it also tracks these measurements over time to give you a larger picture of changes in your fitness score and stress levels. *Sorry iPhone 5 users, looks like you'll be ponying up for an adapter.